Corn, Wheat & Rice Trash Make Concrete Stronger

We've written a lot about alternative fuels, such as using plastics and garbage to power a cement kiln in Texas. Now, in what's at least a three-way win, civil engineers at Kansas State University (KSU) have figured out how to use the waste products of biofuels to make a stronger concrete that's also got a smaller carbon footprint.

Since concrete is one of the world's most-used industrial materials, there's been ongoing work to make it greener. Most efforts are aimed at finding a replacement for Portland cement, one of concrete's main ingredients. For example, Wagners Composite Fibre Technologies, which makes engineering composites, also makes Earth Friendly Concrete (EFC). By eliminating Portland cement, this concrete's carbon emissions are 80 to 90 percent lower than the levels usually associated with that material.

EFC uses a geopolymer binder system made from the chemical activation of blast furnace slag, which is waste from iron production, and fly ash, which is waste from coal-fired power generation.

The KSU researchers have also found a replacement for Portland cement, but they're using ash that results from the waste products of biofuels, in turn made from the waste products of agriculture -- in this case, corn stover, wheat straw, and rice straw. All of these are used as feedstocks for the class of biofuels known as cellulosic, meaning they are derived from feedstock based on inedible waste plant material, instead of feedstock derived from seeds or grains of plants grown as (usually non-food) crops.

Corn stover -- corn stalks and leaves -- is the same material DuPont is using in its Nevada, Iowa biofuel facility, which it expects to complete in 2014.

Since the production of cellulosic ethanol is expected to increase, so will the wastes resulting from those processes, say Feraidon Ataie, doctoral student in civil engineering, and Kyle Riding, an assistant professor of civil engineering, in an article (subscription or payment required) detailing their work in the Journal of Materials in Civil Engineering. That means that the availability of high-lignin residue, the byproduct of cellulosic ethanol, will continue to increase as a feedstock.

At present, this material doesn't have many other uses. It's usually burned to produce electricity, or the ash that results from burning is tossed out and landfilled.

The team found that, after pre-treating the high-lignin ash byproduct, adding it to cement made the cement stronger because the ash reacted chemically with the cement. After some experimentation, they determined that using the agricultural residue ash (ARA) to replace 20 percent of the cement by mass increased the concrete's strength by 32 percent. Ataie and Riding also spent considerable time studying the effects of thermochemical pretreatments to make the ash reactive in specific ways.

According to the article, the team found that:

Pretreatments are effective in partial removal of alkali metals and other impurities out of both wheat straw and rice straw leading to ARA with lower loss on ignition (LOI), higher internal surface area, and higher amorphous silica content than that of unpretreated ARA. It was shown that the ash alkali content correlated with the ash LOI and amorphous silica content.

It makes sense that research that reduces the carbon footprint of cement, makes that cement a lot stronger, and keeps lignin ash out of landfills is taking place in an agricultural state like Kansas. It will also be interesting to see how, and when, this innovation can reduce the cost of making ethanol biofuels by giving commercial value to what was once a waste product.

Very interesting, Ann. Nice use of waste materials, especially since everything usable has already been squeezed from these materials. I also like that it's non-food materials that are going into the concrete.

Rob, the whole second-generation phase of biofuels is surprisingly unknown to many people, especially here in the US. That second generation is the use of non-food crops, on soil that can't be used for food crops, etc. etc.

You're right, Ann, that second generation of biofuels isn't getting the same coverage as the first generation. It's good to see this new industry is turning to non-food crops grown on non-food-ready soil.

Thanks for presenting a different side about how the refuse from these crops can be reused, Ann. I didn't realize there was this type of research being done, but it's good to see! Anytime natural waste materials can be reused to improve something else, that's a good thing.

Elizabeth, what I really liked about this one was the multi-win-win strategy. Keep a potential pollutant out of landfills, use something that's otherwise thrown away (=trash) to squeeze even more value out if it (aka recycling of a sort), make a better product with it that's also got a better carbon footprint than the previous ingredient, and help farmers make more $$ by selling the cellulosic trash instead of paying to have it hauled away. Now--how do we apply this model elsewhere?

Elizabeth, the model of using waste plant material for making biofuel and bioplastics is already well underway, as we've covered in several posts in DN. One is the DuPont story about biofuel:http://www.designnews.com/author.asp?section_id=1392&doc_id=257126Another is using cane trash to make bioplastics:http://www.designnews.com/document.asp?doc_id=237554

I would have thought it would be better to turn any such "waste" under to replenish the organic material in the soil. Since it is cellulosic, I would think this would also help keep the soil loose. This should make it a little less important to put synthetic fertilizers on the ground the next spring.

Not all farmers want to recycle this stuff, for several different reasons (one being that cellulosic material doesn't make very good fertilizer, which has very specific chemical requirements, as any gardener knows). Some of them are covered in the story we did on DuPont using corn stover for making biofuel--we gave the link in this story, but here it is again http://www.designnews.com/author.asp?section_id=1392&doc_id=257126

All gardeners know what they buy in a store - the synthetic, or maybe not, fertilizers I mentioned - have specific chemical requirements. Good gardeners also swear by leaf mold: cellulosic material partly consumed by mold that they turn under in the spring to give the soil more tilth. Sounds like what we're taking away from the soil this way.

You're absolutely right about "specific chemical requirements," which is what I said. But there's cellulosic and then there's cellulosic: they're by no means all the same. And the stuff we're writing about here is not leaf mold--which, BTW, can also vary widely in chemical content (for example, high tannin content in oak leaves). Depending on its chemical composition, some cellulosic material adds nitrogen and other nutrients to the soil, some takes those out, and some doesn't do anything nutritionally, but does add bulk and loft, which is not always needed or wanted, BTW. The stuff being recycled here doesn't add much in the way of nutrients and/or can leach it out. It can also cause rot problems. This is a complex subject, which we touched on in the DuPont article. Check it out.

I had read the DuPont article and I re-read it. I have four comments.I own some DuPont stock so I wish them well.I design concrete structures and I like what pozzolans do, so I'm happy to have more sources.They and you talk to farmers other than those I see either making silage from cornstalks or plowing it under - or both, which is the primary similarity - they don't leave much in the field. I don't see any having trouble getting rid of such "waste." I've never talked to any who had any such "waste," either. They will often plant a rye cover crop over the winter for erosion control and to have something green to turn under in the spring, so the corn from last year doesn't "interfere with corn planting." Maybe this is it: they rotate their crops every few years; from the comment that the stover can "house insects and diseases that damage corn plants" it sounds like the Iowa farmers just grow corn.I mentioned this to my 12th-grade daughter who had an immediate and strong reaction: "Anyone who takes AP Environmental Science knows that one wants to use any organic matter they have in their soil." She has that class this year.

Excellent use for recycled materials. Concrete has been reinforced for eons to make it stronger or lighter. From adding straw to mud bricks in thy neighbors hut, steel rebar in just about everything cast concrete, to adding limestone or pumice (lavarock) in the concrete domed cielings of ancient structures such as the Parthenon. A building which has survived earthquakes and other factors for 1900+ years...

When I was in grad school the civil engineers would enter the annual concrete canoe contest where the teams would have to build a canoe entirely out of conrete and then race it against those of other teams. Most broke up or sank before the finish line, but the builders did use unusual fillers to reduce the density. One mix had a specific gravity of just 0.75, about equal to oak, and it had an amazing tensile strength, almost two percent that of oak.

Evidently this ash is much different from "just a filler", used to reduce density. Foam peanuts are a filler that reduces density but does not add strength. The ash somehow enters into the chemical structure, which is totally different.

j-allen, on first reading, your story about concrete canoes sounds like a cross between a Mafia movie and one about college students' jokes. OTOH, I know these things are real, because there's a cement ship on the beach south of the Santa Cruz harbor. According to the local history I've heard, this one was originally built as a supply ship in 1918, and then got towed over here to become an entertainment spot. Here's the history:http://www.santacruzsentinel.com/ci_17234906and here's a better photo (scroill down a ways):http://www.beachcalifornia.com/cement-ship-seacliff-beach.html

I can back up J-Allen's story. When I was in engineering school, our civil engineering students also had a concrete canoe contest. Either it's a common practice for civil engineering students, or J-Allen and I went to the same school (University of Illinois at Chicago).

Many of the new adhesives we're featuring in this slideshow are for use in automotive and other transportation applications. The rest of these new products are for a wide variety of applications including aviation, aerospace, electrical motors, electronics, industrial, and semiconductors.

A Columbia University team working on molecular-scale nano-robots with moving parts has run into wear-and-tear issues. They've become the first team to observe in detail and quantify this process, and are devising coping strategies by observing how living cells prevent aging.

Many of the new materials on display at MD&M West were developed to be strong, tough replacements for metal parts in different kinds of medical equipment: IV poles, connectors for medical devices, medical device trays, and torque-applying instruments for orthopedic surgery. Others are made for close contact with patients.

Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.